With the proliferation of the Internet, the number of online services that provide various services via the Internet is explosively increasing. In online services, users are generally authenticated using passwords. However, as the number of online services to be used increases, users tend to reuse the same password or two or three passwords in a plurality of online services.
When passwords are reused in a plurality of online services, if one password is leaked, there is a vulnerability of damage increasing in a cascade. In recent years, as disclosed in Patent Literature 1, technology in which, even if a password is leaked, the password is not improperly used by others according to two-step authentication and a master password has been disclosed.